The rapist is very likely to at least have a knife on him (think about it - I won't write how easy it is to obtain).

During the rape he will threaten to use the knife. You could put him in a guard - and he will just try to cut off your legs :-/

Given such circumstances, the predator is always in advantage, and the human pray has little chance. However, training any M.A. is likely to cause the predator to decide on choosing another prey - just because of your stance and environmental awareness (if you don't use that - you aren't really learning M.A. for S.D.). It may not solve the raping problem, but it can save the particular person.